Disk drives are commonly used in workstations, personal computers, laptops and other computer systems to store large amounts of data in a form that can be made readily available to the user. In general, a disk drive comprises a magnetic disk that is rotated by a spindle motor. The surface of the disk is divided into a series of data tracks. The data tracks are spaced radially from one another across a band having an inner diameter and an outer diameter. Each of the data tracks extends generally circumferentially around the disk and can store data in the form of magnetic transitions within the radial extent of the track on the disk surface. Typically, each data track is divided into a number of data sectors that store fixed sized data blocks.
A head includes an interactive element, such as a magnetic transducer, that is used to sense the magnetic transitions to read data, or to transmit an electrical signal that causes a magnetic transition on the disk surface, to write data. The magnetic transducer includes a read/write gap that positions the active elements of the transducer at a position suitable for interaction with the magnetic transitions on the surface of the disk, as the disk rotates.
As known in the art, the magnetic transducer is mounted by the head to a rotary actuator arm and is selectively positioned by the actuator arm over a preselected data track of the disk to either read data from or write data to the preselected data track, as the disk rotates below the transducer. The head structure includes a slider having an air bearing surface that causes the transducer to fly above the data tracks of the disk surface due to fluid currents caused by rotation of the disk.
One part of the motors used in disk drives is the bearing. The basic fluid dynamic bearing involves parts which must move relative to one another, such as a shaft and a sleeve or a thrust plate and a housing, separated by a small gap filled with a viscous fluid such as oil. One characteristic of fluid dynamic bearings is stiffness, which is a measure of the amount of displacement per unit force applied to the rotating element. The force could be due to gravity, an imbalance in the rotating element, or some other source. Another characteristic of fluid dynamic bearings is drag, which refers to the torque required to rotate the rotating element at a rated speed.
One problem with the fluid dynamic bearing is that the stiffness of the bearing is very sensitive to changes in temperature. This is because the stiffness depends on the viscosity of the bearing fluid, and the viscosity of the bearing fluid typically changes with temperature. The bearing drag is proportional to viscosity, and also varies significantly with temperature. In certain applications, such as the use of the fluid dynamic bearing in a disk drive motor, the bearing must operate over a wide range of temperature. As a result, a fluid dynamic bearing with adequate stiffness at one temperature will have a stiffness which is too high at lower temperatures, and too low at higher temperatures, making the fluid dynamic bearing unsuitable for such an application. The same problem occurs with respect to drag.
Prior art fluid dynamic bearings have the problem that stiffness and/or drag are highly dependent on temperature, making conventional fluid dynamic bearings unsuitable for certain applications, such as use in disk drives, VCR helical scanners, gyros, and other rotating devices. There is a need for a fluid dynamic bearing with a reduced dependence of stiffness and/or drag on temperature.